The head of Israel’s centrist Labor Party has ruled out serving in a government led by Prime Minister Benjamin Netanyahu after this month’s general elections.

Netanyahu’s hawkish Likud Beiteinu list has fallen in polls ahead of the Jan. 22 vote, but is still positioned to lead the next government.

Labor leader Shelly Yachimovich vowed Thursday not to join a Netanyahu-led coalition. The move would rob Netanyahu of a potential moderate partner and make it more likely for him to team up with hardliners.

Yachimovich says the slipping support for Netanyahu, to the benefit of a hardline pro-settlement Jewish Home party, has radicalized the prime minister’s list.